Pressure switch with low-pressure cut-off



Oct. 3, 1967 J. J. ZELLER PRESSURE SWITCH WITH LOW-PRESSURE GUT-OFF 2 Sheets-Sheet 1 Filed 001:. 22, 1965 /fl/VE/VTOR JOSEF J. ZE LLER 1957 J. J. ZELLER PRESSURE SWITCH WITH LOW-'PRESSURE CUT-OFF Filed Oct. 2-2, 1965 '0 9 k L/OSEF d ZELLER 8Y9! f. Hi5

United States Patent ()fifiee 3,345,480 PRESSURE SWITH WITH LOW-PRESSURE CUT-OFF Josef J. Zeller, Asheville, N.C., assignor to Square 1) Company, Park Ridge, 111., a corporation of Michigan Filed Oct. 22, 1965, Ser. No. 501,308 6 Claims. (Cl. 200-83) ABSTRACT OF THE DISCLOSURE A fluid pressure responsive electrical switch having contacts which open when the switch is subjected to a high pressure, which close when the pressure decreases to an intermediate value, and which reopen upon a further reduction of the pressure to a predetermined low value. A pressure responsive operating lever causes a snap-acting mechanism to open and close the switch contacts at predetermined high and intermediate pressures, respectively, and engages a separate low-pressure release lever under conditions of predetermined low pressure to cause the release lever, in turn, to engage a movable contact supporting frame and to reopen the switch contacts.

This invention relates to electrical pressure switches, and more particularly to an electrical pressure switch which opens its contacts when subjected to high pressure, closes its contacts when the pressure decreases to an intermediate value, and reopens its contacts upon reduction of the pressure to a predetermined low value.

A principal object of the invention is to provide such an electrical pressure switch having improved means for opening its contacts upon the pressure falling below the low value.

The foregoing object is accomplished by the provision, in a pressure switch, of a low-pressure release lever fulcrumed intermediate its end portions and engaged, under conditions of low pressure, near one end portion by an operating lever of the switch to move the other end portion thereby to cause a contact operating mechanism of the switch to open the contacts of the switch. In the preferred embodiment, the low pressure release lever has an offsetting portion passing through an opening in a base plate of the switch and the lever is fulcrumed on an edge of the opening.

Other objects and advantages of this invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a top plan view of a pressure switch in accordance with this invention, the switch being shown in the intermediate-pressure, contact-closed position and having portions removed for clarity;

FIG. 2 is a sectional view looking toward the front of the switch and taken generally along the line 2-2 of FIG. 1;

FIG. 3 is a fragmentary sectional view taken generally along the line 3-3 of FIG. 1, but with the switch in the high-pressure, contact-open position;

FIG. 4 is a fragmentary sectional view taken generally along the line 44 of FIG. 2;

FIG. 5 is an enlarged side elevation, partially in section, showing the operating mechanism of the pressure switch of FIG. 1 in the intermediate pressure, contactclosed position; and

FIG. 6 is a perspective view of a low-pressure release lever which forms a part of the switch of FIGS. 1 through 5.

7 Referring to the drawings, a pressure switch in accordancewith the present invention includes a supporting frame 10 comprising a base plate 11 and a pair of integral upstanding brackets 12 and 13 at opposite sides of the 3,345,483 Patented Oct. 3, 1357 base plate 11. The brackets 12 and 13 have respective inwardly-extending arm portions 14 and 15 to which a terminal block 16 is secured as by a pair of screws 17. A plurality of barrier walls 18 formed integrally with the terminal block 16 define four compartments in each of which there is mounted a terminal and contact member 19 by means of an associated screw 20. As shown best in FIG. 3, each of the contact members 19 is generally L- shaped and has a terminal screw 21 threaded into one leg portion and a fixed contact 22 suitably secured to the other leg portion.

Near its front edge, the base plate 11 supports a pair of upwardly-extending posts 24 and 25. A range spring 26 disposed about the post 24 has its upper end bearing against a spring retainer 27 captivated by a nut 28 threaded on the post 24. The lower end of the range spring 26 abuts against, and applies a force to, a free front end portion of a generally channel-shaped operating lever 29 having a relatively large, generally central opening 29a and a pair of openings adjacent the front end portion through which the posts 24 and 25 extend, respectively. The amount of force applied by the spring 26 to the lever 29 is determined by adjustment of the nut 23. A curved rear end portion 29b of the operating lever 29 is pivotally received in suitable slots 31 (FIGS. 2 and 3) in the arm portions 14 and 15, respectively.

As shown in FIGS. 3 and 4, a contact operating mechanism comprises a helical toggle spring 33, a U-shaped toggle link 35, and a movable contact frame 36. One end of the spring 33 is connected to the front end portion of the operating lever 29 by means of a small aperture provided therein, and the other hooked end of the spring 33 is similarly connected to the toggle link 35. The link 35 is pivotally mounted on the movable contact frame 36 to an upper surface of which is riveted a bracket 37. A double-armed movable contact carrier 38 is riveted to, and extends upwardly from, an upstanding portion of the bracket 37.

The legs of the toggle link 35 have respective outwardly-turned portions provided with knife edges received in respective V-shaped notches formed in spaced depending arms 39 of the contact frame 36 (best seen in FIG. 5) thereby to provide the pivotal mounting between the link 35 and the contact frame 36. The contact frame 36, in turn, is pivotally mounted on the frame 1! by an additional pair of depending arms 40 having respective tip portions received in suitable depressions in a pair of spaced ears 41 which project upwardly through the opening 29a from an embossed or raised portion 42 of the base plate 11. One of the depending arms 49 has an extension 43 which extends beyond the arm portion 14 of the bracket 12 to provide a stop for the contact frame 36 in the contact-open position as will be subsequently explained.

As shown in FIG. 2, the rear portion of the movable contact frame 36 is shaped to provide a generally square opening 44 through which the bight portion of the U- shaped toggle link 35 projects. The bracket 37 is provided with an adjustable depending arm 46 which overlies the square opening 44 and which is disposed above the bight portion of the toggle link 35 thereby to limit the upward movement of the link 35 within the opening 44.

Each of the arms of the contact carrier 38 is provided with a resiliently-mounted contact bridge 48 having contact portions disposed at opposite ends thereof for engagement, respectively, with the fixed contacts 22.

As shown in FIG. 5, the post 25 is provided with a shoulder against which a cup washer 53 is normally biased by a spring 54. The spring 54 is adjustably compressed by a nut 55 threaded on the post 25 and bearing against a second cup washer 56 positioned at the upper end of the spring 54.

A cover 66 is provided to protect the operating mechanism and includes an aperture receiving the upper end portion of the post 24. A cover nut 67 is threaded on the post 24 to maintain the cover 66 in place.

A pressure plate 68 (FIGS. 3 and 5) having a pair of spaced upstanding arms 69 extending through apertures provided in the embossed portion 42 of the base plate 11 engages respective spaced notches 70 (FIG. 5) formed in the operating lever 29. The pressure plate 68 rests upon a diaphragm 68a which is sealably secured at its margin between the base 11 and a flanged cup 68b. The diaphragm 68a and pressure plate 68 comprise means responsive to variations in pressure of a fluid in a conduit 71 for rocking the operating lever 29 about its pivotal axis.

During use, opposite sides of a power line (not shown) are connected to the outside pair of the terminals 19, as viewed in FIGS. 1 and 2, by the screws 21; and, conductors (not shown) leading to a load such as an electric motor driving a pump are connected to the respective inside pair of terminals 19 by the screws 21. The load is therefore connected to the power line through a circuit completed when the pairs of contact portions of the movable contact bridges 48 engage their complementary pairs of the fixed contacts 22.

When the pressure in the conduit 71 is at a preselected intermediate value, the switch is in the closed position of FIGS. 1, 2, and 5. Upon the pressure in the conduit 71 increasing, the pressure plate 68 presses against the operating lever 29 and rotates it about its pivotal mounting in the slots 31 against the bias of the spring 26, thereby to raise the end of the toggle spring 33 which is attached to the operating lever 29. With further increase in pressure, the operating lever 29, continuing its upward movement, engages the undersurface of the cup washer 53 and lifts the washer 53 from its seat whereby the bias of both of the springs 54 and 26 combine to oppose the upward movement of the lever 29. When, at a preselected high pressure value, the lever 29 has been raised to a position causing the spring 33 to pass over center, the bight portion of the toggle link 35 moves upwardly with a snap action so that the contact frame 36 and the contact carrier 38 rotate in a counterclockwise direction, as viewed in FIG. 5, about the depending arms 40. This action is accompanied by a hammer blow imparted to the contact frame 36 by the bight portion of the link 35. Such rotation of the contact carrier 38 causes the contact bridges 48 and their associated movable contact portions to be rapidly moved to an open-contact position breaking the circuit through the switch. As will be seen from FIG. 3, the open position of the contacts is limited by the interengagement between the extension 43 of the contact frame 36 and a shoulder formed on the arm 14. The distance through which toggle link 35 travels during the opening of the switch is determined by the position of the arm 46 of the bracket 37. The arm 46 may be bent to provide adjustment.

Upon a decrease in pressure from the high pressure value, the force exerted by the pressure plate 68 on the operating lever 29 decreases and the operating lever 29 then moves downwardly under the influence of springs 26 and 54 until the cup washer 53 again seats. Thereafter, the bias of only the spring 26 acts upon the operating lever 29.

As the lever 29 continues to move downwardly with decreasing pressure in the conduit 71, the end of the toggle spring 33 attached to the operating lever 29 moves downwardly through a dead-center position causing the toggle link 35 to snap downwardly. The force exerted by the toggle link 35 at the point of its pivot on the depending arms 39 of the contact frame 36 causes the contact frame 36 to move from the contact-open position of FIG. 3 to the contact-closed position of FIG. 5 with a snap action. The bight portion of the link 35 aids this closing movement by striking a hammer blow against the lower wall portion of the rectangular opening 44 in the frame 36.

Inasmuch as the bias of both of the springs 26 and 54 operate against the operating lever 29 when the contacts open, and only the bias of the spring 26 operates against the operating lever 29 when the contacts reclose, it will be seen that changes in the operating differential of the switch may be accomplished by varying the bias of the spring 54. This is effected, as previously described, by adjusting the position of the nut 55.

A pressure switch similar to the one thus far described is disclosed in C. A. Schaefer Patent No. 2,741,678 which issued April 10, 1956. In the switch of the Schaefer patent,the lever 29 continues to move in the downward direction with decreasing pressure in the conduit 71 and the contacts of the switch remain closed. With the contacts closed, a pump motor controlled by the switch would operate. Normally, this would cause the pressure to increase and eventually the switch would open as described above. If there were a failure of the fluid supply, however, no pressure increase would occur, the switch contacts would remain closed, and the motor would continue to operate to no avail. Since many pump and motor combinations are designed for intermittent service, this could cause overheating of the motor or pump or both. Therefore, it is desirable that the pressure switch have means providing a low-pressure cut-off whereby the switch contacts will reopen under conditions of predetermined low pressure to discontinue operation of the motor. The.

switch of the present invention provides this low pressure cut-off feature and accomplishes this result as will now be described.

As shown best in FIGS. 5 and 6, a low-pressure release lever 72 has an intermediate offsetting portion 74 bent at right angles with respect to offset front and rear portions 75 and '76. The front portion 75 is disposed between the base plate 11 and the front portion of the operating lever 29 in the path of movement thereof, the front portion 75 being bifurcated to permit the release lever 72 to clear the post 24 as seen in FIG. 4. The offsetting portion 74 passes through an opening 78 in the embossed portion 42 of the base plate 11 so that the rear portion 76 extends along the undersurface of the embossed portion 42, the lever 72 being fulcrumed on an edge 79 of the opening 78.

Because the offsetting portion 74 and the rear portion 76 are narrower than the front portion 75, a pair of shoulders 75a is defined on the front portion 75 at its junction with'the offsetting portion 74. The shoulders 75a aid in maintaining the lever 72 properly positioned in the opening 78.

An upwardly-bent operating portion 80 of the rear portion 76 is positioned to pass through an opening 81 in the embossed portion 42 for engagement with the lower edge face of the contact frame 36.

Thus, in the switch of this invention, upon loss of fluid and decrease in pressure to the predetermined low value, further downward movement of the operating lever 29 occurs after the contacts of the switch have closed and eventually the front portion of the operating lever 29 engages,

the front portion 75 of the low-pressure release lever 72 and rocks the lever 72 about its fulcrum on the edge 79 causing the operating portion 80 of the rear end portion end portion 86 (FIG. 1) engageable with the front end portion of the operating lever 29 and which, when the crank 84 is rotated approximately 30, lifts the operating lever 29 so as to release the lever 72 and to permit reclosure of the switch contacts by the contact operating mechanism. So long as the crank 84 is manually main tained in this position, the switch contacts remain closed and a motor-operated pump controlled by the switch will operate. When the pressure in the conduit 71 has in creased to a value above that at which the low pressure cut-off had occurred, the crank 84 can be released and the switch will function as previously described, opening its contacts when the pressure reaches the preselected high pressure value.

The crank 84 also may be rotated to a self-maintained position, about 90 from that shown, in which its inner end portion 86 is over-center with respect to the operating lever 29. In this position, the inner end portion 86 engages a shoulder on the collar 85 and the crank 84 maintains the operating lever 29 in a raised position wherein the contacts are open. Thus, the crank 84 also provides a means for maintaining the switch in an inoperative, or OFF, condition when desired.

I claim:

1. In a pressure switch having separable contacts and a supporting frame, an operating lever pivoted on said frame and movable in response to variations in pressure to which the switch is subjected, a mechanism operated by said operating lever for causing opening and closing of said contacts at preselected high and intermediate pressures, respectively, the improvement comprising a lowpressure release lever fulcrumed intermediate its ends on said frame and having a first end portion in the path of movement of said operating lever and a second end portion positioned to engage said mechanism upon movement of said first end portion in one direction, said operating lever under conditions of predetermined low pressure engaging said first end portion of said release lever and moving it in said one direction thereby causing said second end portion of said release lever to engage said mechanism, said engagement of said second end portion with said mechanism causing said mechanism to open said contacts.

2. A pressure switch in accordance with claim 1 wherein said low-pressure release lever includes an offsetting portion intermediate said first and second end portions, and said frame includes a base plate having an opening through which said offsetting portion passes, whereby said end portions are disposed on opposite sides of said base plate, respectively.

3. A pressure switch in accordance with claim 2 wherein said low-pressure release lever is pivoted on an edge of said opening.

4. A pressure switch in accordance with claim 3 wherein said offsetting portion and one of said end portions of said low-pressure lever are narrower than the other end portion thereby defining, on the other end portion at its junction with said offsetting portion, a pair of shoulders which aid in maintaining the low-pressure lever positioned on said edge.

5. A pressure switch in accordance with claim 2 wherein one of said end portions of said low-pressure release lever has a bent operating portion extending toward the side of said base plate on which the other of said end portions is disposed.

6. In a pressure switch, a supporting frame, an insulating block mounted thereon, fixed contacts on said block, movable contacts cooperating with said fixed contacts, a movable contact frame pivotally mounted on said supporting frame and carrying said movable contacts, a toggle link pivoted on said contact frame for moving said contact frame between open and closed positions of said contacts, an operating lever pivoted on said supporting frame, a toggle spring connecting said toggle link and said operating lever, biasing means biasing said operating lever toward one position, pressure responsive means for pivoting said operating lever with and against the bias of said biasing means, the line of action of said toggle spring being moved across the pivot point of said toggle link by pivotal movement of said operating lever to effect a rapid overcenter movement of said toggle link, means on said contact frame for determining the limit of travel of said toggle link including a first portion determining a closed-contact position of said link and a second portion determining an open-contact position of said link, a low-pressure release lever pivoted on said supporting frame and engageable by said operating lever, upon a decrease in pressure and after said toggle link has moved to its. closed-contact position, to move said contact frame to said open position of said contacts.

References Cited UNITED STATES PATENTS 2,741,678 4/1956 Schaefer et al. 200-83 BERNARD A. GILHEANY, Primary Examiner. H. B. GILSON, Assistant Examiner. 

1. IN A PRESSURE SWITCH HAVING SEPARABLE CONTACTS AND A SUPPORTING FRAME, AN OPERATING LEVER PIVOTED ON SAID FRAME AND MOVABLE IN RESPONSE TO VARIATIONS IN PRESSURE TO WHICH THE SWITCH IS SUBJECTED, A MECHANISM OPERATED BY SAID OPERATING LEVER FOR CAUSING OPENING AND CLOSING OF SAID CONTACTS AT PRESELECTED HIGH AND INTERMEDIATE PRESSURES, RESPECTIVELY, THE IMPROVEMENT COMPRISING A LOWPRESSURE RELEASE LEVER FULCRUMED INTERMEDIATE ITS ENDS ON SAID FRAME AND HAIVNG A FIRST END PORTION IN THE PATH OF MOVEMENT OF SAID OPERATING LEVER AND A SECOND END PORTION POSITIONED TO ENGAGE SAID MECHANISM UPON MOVEMENT OF SAID FIRST END PORTION IN ONE DIRECTION, SAID OPERATING LEVER UNDER CONDITIONS OF PREDETERMINED LOW PRESSURE EN- 